Device for measuring levels

ABSTRACT

A device for measuring fill levels, in particular liquid fill levels, is provided, which device has a capacitive sensor and, connected to the sensor, a unit for analyzing a measuring signal from the sensor. The device for measuring fill levels may be manufactured cost-effectively and enables highly accurate measurements. The sensor has at least two base components including finger-shaped electrodes projecting therefrom. The electrodes are situated offset from one another, and the base components are fixed in position with respect to one another by at least one fixing element, the fixing element being situated outside the overlapping area of the electrodes.

FIELD OF THE INVENTION

The present invention relates to a device for measuring fill levels, andrelates particularly to a device for use as a fill level sensor forliquids.

BACKGROUND INFORMATION

Different fill level sensors which utilize different physical effectsare known in the art. A capacitive sensor having a changeable dielectricis a possible design, in which, during a change in the fill level, thedielectric proportion of the medium to be measured changes within thecapacitor, thereby causing a capacitance change. The fill level may bedetermined based on the capacitance change. Plate capacitors or flatcapacitors (inter-digital structures) designed on the basis of printedboards or punchings are possible, in addition to a design utilizing acylinder capacitor having the appropriate coaxial structures.

The object of the present invention is to provide a device for measuringfill levels which may be manufactured cost-effectively and which enablesmeasuring as accurately as possible.

SUMMARY

The present invention provides a sensor using two base components, fromeach of which project finger-shaped electrodes, offset from one another.In this manner, a total capacitance of the device is achieved bymultiplying the single capacitances by the number of electrode pairs,thereby approximately achieving a proportional ratio of the pairs ofelectrodes, submerged in the medium, to the total capacitance. Using afixing element, the base components are positioned with respect to oneanother in such a way that a continuous allocation takes place among theelectrodes, and such that a minimum interfering proportion of othermaterials is situated between the electrodes, in order to achievehighest measuring accuracy as possible. Furthermore, rapid flow-off ordischarge of the medium during fluctuating fill levels is achieved dueto the open structure in the overlapping area of the electrodes, so thata swift response to changing fill levels may take place.

An example embodiment of the present invention provides that the sensorhas a meander-shaped inter-digital structure, whereby a simplecomputation of the total capacitance during changing fill levels may bepossible. Inter-digital structure means that there are spaces betweenthe finger-shaped electrodes, into which spaces correspondingfinger-shaped electrodes of another base component may be inserted orintroduced. There is still a gap between the electrodes of the two basecomponents, which gap is filled by the medium to be measured. Ameander-shaped path, facilitating a flow-off of the medium to bemeasured during fill level changes or fluctuations, is formed due to themeandering path of the gaps between the electrodes.

To achieve a design that is as compact as possible, it is providedaccording to the present invention that the electrodes of the basecomponents are situated essentially in a plane, so that the sensor has aplanar structure.

To improve the flow-off characteristics of the medium to be measured, itis provided according to the present invention that the electrodes aretapered starting from the base component, thereby additionally improvingthe electrodes's mechanical stability.

Manufacturing the fixing element by using plastic injection molding orplastic extrusion coating is a cost-effective way of aligning theelectrodes and the base components to one another, with which methodgreat quantities of sensors having sufficient accuracy may bemanufactured. Great position accuracy of the base components, and thusof the electrodes, is achieved by designing the fixing element as aframe, in particular as a closed frame; the frame may also bemanufactured by using plastic extrusion coating. Since the extrusioncoating material is not situated in the overlapping area of theelectrodes, i.e., between the electrodes, the extrusion coating materialdoes not act as a dielectric, and thus the total capacitance, and inturn the measuring accuracy, is not affected.

In order to manufacture the sensor as cost-effectively as possible, itis provided that the base component and the electrodes are manufacturedfrom a pressed screen, e.g., in one piece, the pressed screen being madeof a metal which has robust characteristics in the medium surroundingit. As an alternative to such a material selection, the electrodes andoptionally the base component may be coated with a protective coating toprotect the electrodes against corrosive media.

BRIEF DESCRIPTION OF THE DRAWING

Figure shows a schematic representation of a measuring device accordingto the present invention.

DETAILED DESCRIPTION

The figure shows a schematic representation of a sensor 1, which is madeup of two base components 2, 3, from each of which electrodes 20, 30project in one direction. Electrodes 20, 30 are situated in a plane inthe illustrated exemplary embodiment; alternative embodiments oralternative spatial positioning of electrodes 20, 30 may also beprovided. Electrodes 20, 30 of both base components 2, 3 face each otherand are situated offset from one another in such a way that ameander-shaped gap forms between electrodes 20, 30, into which gap amedium (not shown), a liquid, for example, may penetrate. As a result ofthis medium's penetration, the total capacitance of sensor 1 changes dueto the medium's different dielectric constant in relation to air.Depending on the fill level, the capacitance between the pairs ofelectrodes thus changes; an electronic unit (not shown) analyzes thecapacitance signal and conveys it to a display device or regulates asystem correspondingly based on the measured value.

Outside the overlapping area of electrodes 20, 30, i.e., the area inwhich electrodes 20, 30 do not mesh with one another, a circumferentialframe 4 is injection molded onto base components 2, 3 to reliably andinexpensively fix electrodes 20, 30 in position. Finger-shapedelectrodes 20, 30 are thus supported on one side on the respective basecomponents 2, 3 and, due to frame 4, the plastic proportion betweenelectrodes 20, 30 is negligibly small with regard to the electriccapacitance. This, in particular, has the advantage of providingincreased measuring accuracy, since conventional plastics have a hightemperature sensitivity with respect to the relative dielectricconstants, so that, in the presence of plastic materials between theelectrodes, great non-linear changes in the partial capacitance andgreat non-linear temperature changes make an exact analysis of the filllevel difficult.

The planar structure according to the present invention providesfree-standing electrodes 20, 30 in the overlapping area, thereby makingthe plastic proportion negligible with respect to the capacitance, andat the same time, a meander-shaped gap is achieved between electrodes20, 30, through which gap the flow-off of the liquid or the medium isdefinitely improved. In the exemplary embodiment illustrated, electrodes20, 30 are tapered starting from the particular base component 2, 3(W1>W2), whereby the mechanical stability of electrodes 20, 30, as wellas the flow-off characteristics, are further improved.

The structure of sensor 1 may be produced using a pressed screen which,for fixing purposes, is extrusion-coated with a closed or open plasticframe 4. Provided that frame 4, and thus the entire measuringcapacitance, is submerged into the medium to be measured, sensors fordetecting the relative dielectric constants may also be implemented inthis way.

1-8. (canceled)
 9. A capacitive sensor device for measuring a fill level of a medium, the sensor device being connected to an analyzing unit for analyzing a measured signal from the sensor, the sensor device comprising: at least a first base component and a second base component, wherein each base component has a plurality of projecting finger-shaped electrodes that are laterally offset from one another, and wherein the projecting electrodes of first base component are positioned in opposing orientation to the projecting electrodes of the second base component such that the projecting electrodes of the first and second base components at least partially overlap; and at least one fixing element for fixing the first and second base components in position with respect to one another, wherein the fixing element is positioned outside of an area where the projecting electrodes of the first and second base components overlap.
 10. The sensor device as recited in claim 9, wherein the sensor device has a meander-shaped inter-digital structure.
 11. The sensor device as recited in claim 10, wherein the electrodes of the first and second base components are situated substantially in a common plane.
 12. The sensor device as recited in claim 10, wherein the electrodes of the first and second base components are tapered starting from the end attached to the respective base component.
 13. The sensor device as recited in claim 11, wherein the electrodes of the first and second base components are tapered starting from the end attached to the respective base component.
 14. The sensor device as recited in claim 11, wherein the fixing element is formed by one of plastic injection molding and plastic extrusion coating.
 15. The sensor device as recited in claim 9, wherein the fixing element is a frame.
 16. The sensor device as recited in claim 11, wherein the fixing element is a frame.
 17. The sensor device as recited in claim 12, wherein the fixing element is a frame.
 18. The sensor device as recited in claim 9, wherein the base components and the projecting electrodes are made from a pressed screen.
 19. The sensor device as recited in claim 9, wherein the projecting electrodes have a protective coating.
 20. The sensor device as recited in claim 11, wherein the projecting electrodes have a protective coating.
 21. The sensor device as recited in claim 12, wherein the projecting electrodes have a protective coating. 